1. Field of the Invention
The present invention generally relates to a lithography process, and in particular, to a method for constructing an optical proximity correction (OPC) model.
2. Description of Related Art
Along with the rapid development of semiconductor process technique, further improvement in operation speed and performance of the device is demanded, which needs continuously miniaturizing the size of the whole circuit device and continuously increasing the integration thereof. Usually, as the semiconductor devices develop towards the design of the compact circuit devices, the lithography process is quite important in the whole process.
In the semiconductor process, for the patterning of each film or areas with implanted dopant, the scope thereof is defined and the critical dimension (CD) is determined by the lithography process. In the lithography process, firstly a photosensitive photoresist material layer is formed on a wafer surface. Then, a photoresist exposure procedure and a development procedure are performed in sequence, so as to transfer the wanted pattern to the photoresist material layer on the wafer surface via the pattern of the mask, thereby forming a wanted photoresist pattern. As the devices are continuously miniaturized and integrated, the design of the integrated circuit (IC) becomes increasingly complicated, such that the accuracy of transferring the mask pattern to the wafer is quite important. If the transferring of the pattern does not meet the expectations, the CD on the chip may be impacted.
Under the trend that the line width and the pitch of the device are reduced, the transferring of the pattern may be easily deviated in the exposure procedure, that is, the so-called optical proximity effect (OPE). The accuracy of the lithography imaging may directly affect the yield of the product, and some methods of enhancing the resolution are continuously proposed to solve the foregoing problems. For example, the mask pattern is modified by using the optical proximity correction (OPC), and the main object thereof is to eliminate the CD deviation resulting from the OPE, that is, to reduce the deviation between the photoresist pattern and the mask pattern.
In a conventional OPC, a deviation value is obtained by comparing the original design data having a circuit layout pattern with the photoresist pattern formed by pattern transferring through the mask, and the relative data of different patterns are collected, so as to construct an OPC model. However, in the process of fabricating the mask, when the original design pattern is written on the mask, usually the pattern formed on the mask may have corner rounding because of the natural characteristics of the writing tool, and thus the pattern formed on the mask may not be identical to the original design pattern. Therefore, the OPC model constructed according to the original design pattern cannot modify the device layout design with the deviation caused by the pattern actually formed on the mask.